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MG MGB Technical - Regulator adjustment

Hello, new to the board. I just installed a new Dynasty sealed battery in my positive ground car after cleaning and repainting the boxes then installing those plastic bins. I even went with a heavier gauge cable to the switch relay.
My question for the pros out there is this. The original battery showed signs of overcharging (acid), and I want to know the proper output voltage.
I read at this site (under electrical) that at 3000rpm the voltmeter should read 15 volts or within .3 of that (14.7 to 15.3).
Searching through the archives I read that 14.5 volts should be maximum and have even been told that by others.
I reved my up high (unknown rpm) and found that mine is putting out 15.8 to 15.9 so its obvious that it needs to be turned down, but to what? I cant see how .5 more volts than the 14.7 to 15.3 described at this site would make much difference but it apparently does.
I probably do not have to touch the cut out relay but I will check it.

There is the possiblity that the previous unsealed battery just sloshed around a bit too much back there, but the caps never came off.
I might be splitting hairs here but I do like my lights the way they are, bright.

thanks


Boris

Boris, this is all a bit of a compromise but 14.5 volts is too low for good lighting. On the other hand 15.9 is way over the top and you will boil your battery. Different manufacturers specify different voltages for some reason and the voltage readings are also temperature dependent but have a look at http://nfahc.co.uk/RB340.htm which I'm sure will give you the information you need.
Iain MacKintosh

Dynamos/control boxes generally run higher voltages than alternators/voltage regulators. The former varies quite a bit with temperature, as well as manufacturing and adjustment tolerances, whereas the latter doesn't have temperature sensitivity but still has manufacturing tolerances. In the past I've found web site references to research by the likes of Mercedes Benz saying that some alternator voltage regulators have been found to put out voltages in the region of 14.3v which is insufficient to fully recharge a battery after going flat. As I recall (don't have the books to hand) the workshop manual quotes 14.7 for the alternator, but that starts dropping as soon as any electrical load is applied to the system. Again as I recall 15.3 is at the top end of the temperature and tolerance range, being quite a bit lower (lower than an alternator) at the other extreme of temperature and tolerance.

It is the voltage regulator relay that would need to be adjusted to reduce the peak voltage from 15.9 to 15.3, not the cut-out. After starting, which takes charge out of the battery, the dynamo starts charging which puts it back. It only does this gradually, and the battery voltage rises as it does so. As the voltage approaches the 'fully charged' level the control box reduces the charging current with the voltage regulator relay. This doesn't suddenly operate and stay operated, like the cut-out relay, but operates and releases very rapidly. This can be seen from slight arcing at its contact and a vibration if you touch the relay armature gently. Initially it only reduces the charge for a very short period, much shorter than the full charge period, but as the voltage of the battery continues to rise, but more slowly, the 'off' period increases and the 'on' period reduces, until equilibrium is reached. Depending on the meter you use you may find an analogue instrument gives a steadier reading than a digital.

Probably more than you wanted to know, but if you tweak the voltage regulator relay (which I think is the opposite end of the three relays to the cut-out) to increase its spring tension you should reduce the peak voltage.
Paul Hunt 2

Ther workshop manual is a fountain of wisdom on the regulator. It is well worth checking the control box earth. Also check all other contacts for tightness and good connection, ensure the swamp and field resistors are in place and have continuity If this is good you can set the the voltage regulator and drop off using a DVM. The voltage is set by the cam on top of the relay, this is the left hand one viewed from the front of the box. To set it remove the wires from the B terminals, connect battery and ign coil with a croc lead so you are able to start the car. Remove the WL lead and clip the DVM from there to ground, this gives easy electrical access to the D terminal they are common. Run the engine at 3000 rpm and set the voltage via the cam to be 14.9 to 15.5 v. I set mine to 15.3 .Unsteady readings may be dirty contacts, The contacts buzz faster than you can see and need some overtravel to keep clean. I set mine to .010" when it would not charge and that has worked fine since, with the voltage you have I do not think this is your problem.
See how this goes and get back, you can check the cut out easily but the over current needs a 22A meter so I have never done this, my meters stop at 10A.
Stan Best

thanks all for the info and for the link Iian.

Stan, the instructions I have say to remove only the WL wire and to connect the voltmeter to the terminal. Not the wire?
Do you do this for the access to the D terminal and if so for what purpose?

by the way, the generator (moss) and voltage regulator(Lucas) are both new, so I dont think the contacts are a concern.
My readings are at the starter switch relay accessory spade is 12.7 volts with the engine off and 12.5 to 12.6 at idle (1100rpm +/-). The cutout relay would not be the reason for an overcharge would it? I cant see how.
Boris

from what I have been reading a defective cut out relay would only lead to a discharge situation which would overwork the generator and battery.
Boris

Correction - the charging voltage for a dynamo varies from 14.3 to 14.9v at a temp of 40C/104F, through to 14.9 to 15.5v at a temp of 10C/50F. Makes 15.9v even less excessive, although probably still worth turning down a smidgen if all the connections are good. FWIW the alternator spec is 14.3 to 14.7v at 5000rpm.

From my understanding the relay on the *left* when looking at the front is the cut-out, to adjust the charging voltage you would have to adjust the voltage regulator relay on the *right*. Adjusting the cut-out will vary the cut-in and drop-off voltages, which should be in the range of 12.7 to 13.3 and 9.5 to 11.0 respectively.

With voltage readings of 12.7, 12.5 and 12.6 the dynamo isn't charging at all, probably because the revs aren't high enough - the dynamo doesn't charge at a typical idle as evidenced by the ignition warning light being on or flickering.

The cut-out can't overcharge the battery, but it can discharge it if it sticks, which if the engine is stopped can damage the control box. A sticking voltage regulator will overcharge, but one with dirty contacts will under charge. The third (middle) relay in the MGB control box is the current regulator which protects the dynamo. If this sticks it can overheat and damage the dynamo, if its contacts are dirty it will also undercharge.

Bear in mind that any electrical problem can be intermittent, just because you measure the correct voltage at one point in time doesn't mean it is always going to be the same. If you suspect this connect up your meter so that it sits in the cabin somewhere and you can keep an eye on it while driving.
Paul Hunt 2

The key thing is wires off off the B terminals. Removing the WL only gives you access to the D terminal , they are connected inside trhe control box. All this assumes you are running a dynamo controlled by the 3 coil box on your +ve earth car.
Stan Best

Hi Folks:

I have had this problem with my old 66 B, after I installed a 12 volt battery. Wiped out several Sears batteries, until I put back the twin 6 volt units. Problem went away. That was over 35 years ago. Had the same problem with the 67 B, put in twin 6's and they lasted 8 years. Present twin 6's (Interstate 17HF) working fine. I guess the added impedance of the twin 6's affect the charging voltage. There was special plastic tool that was delvered (in glove box) with 66B when new; which was used to adjust the voltage regulator points. Tool disappeared years ago!

Good Luck: Rich Boris 67 B roadster
Rich Boris

Twin 6v shouldn't be any different to single 12v, both systems have six 2v (nominally) cells in series, they are just packaged differently. Of course if you always had problems with the same make of battery from the same source they could simply have been no good.
Paul Hunt 2

Well it turned out that the generator was actually putting out 16 volts at high rpm and mild weather (65-68 degrees).
Good thing I did check the cutout relay because it turned out the voltage was too low so it would cut out the battery too late and reconnect at too low a voltage. I first had a problem with the cutout because the readings were inconsistent so I cleaned the contact and then readjusted.

So now its putting out 14.78-14.9+ (it may do 15).


By the way, that was a special Odyssey battery #PJ 1200LMJT (brass terminals)with the positive post on the right facing the back of the bin. Probably the best looking battery I have ever seen. It fit much better than the group 26 I had in there and it is a sealed deep cycle. Very nice CCA. You can leave this battery for 2 years or so depending on the weather, and it will still turn the starter. It is the perfect battery.
The cable I used I think was a 1 gauge with copper/tin ends 96" long. Original cable was 94-95" long but you have to allow for the thickness. You will have to replace 4 rubber grommets under the car that the lines run through. Check page 72 of the moss catalog. Thats 4 of item #60 and 1 of item #64.

thanks
Boris

Drop out should be set to between 9.5 and 11 v
Cut in should be between 12.7 and 13.3 v.You must turn on a load, headlamps would be the usual choice .
Don't worry that cut out seems so low, this is intentional and the cut out relay and over current relay introduce some series resisance so that the battery can be at a a floated 14.5v while you are measuring this at the D terminal. The cut will work reliably at these voltages because of the way it is wound.
The only word of warning is never force the cut out contact in while the engine is not running as it will latch on and destroy the control box.
Stan Best

thanks stan. I set the cut in at just what you say using the cam (at 12.7+ to 13.28), and then checked the drop out and it was something like 10+ to 11.28 I think.


I got the battery # wrong . It is a #PC 1200LMJT and here is what it looks like.
http://www.odysseybatteries.com/battery/pc1200lmjt.htm
Boris

Hi, me again. It looks I am going to have to replace that darn regulator because the drop out aspect of the cutout relay is just not consistent.
I was watching the ignition light while idling and at first it would come on only when I slow the engine by depressing the clutch, but it now will not come on at all.

One last thing though. I checked the schematic for a '67 and earlier car to trace the ground lead from the regulator and it ends right behind the left headlight.
I just can not find where this thing grounds. Is it under the slam panel or is it inside the headlight bucket?
Boris

My car is away having some welding done so I can't look at it now.
I did look at the circuit digram and it shows the ground being the one used by the headlights. That one must be somewhere around the bonnet slam panel , the connector to the headlights that goes via a grommet in the inner wings carries main dip and earth. Paul Hunt has a great page about adding relays to headlamp circuits, that may give you a pointer.since the cut out relay current runs to earth through here it would be worth checking. My car idles at 850 rpm, the tacho calls this 950, the charging light is only on very dimly at that rpm. If I set the idle to 750 RPM the warning light is on quite strogly, but it flickers. You may be OK as you are, you can always rig up a DVM to measure the voltage, in or out of the ign switch or the SW on the coil will give you what you want. The big deal with the cut out is. Does it come on when you stop the engine but leave the ign on ?
Stan Best

Yes it does come on (brightly) when I go to switch the key to run without starting the engine.

Stan you sparked something and it got me thinking (pun intended). My original thinking was that the purpose of the drop out aspect of the cut out relay is to keep the battery from discharging through the generator, both while running and not. But if mine idles around 12.5 volts (+/-) with out headlights, and high 11's to low 12's with, what happens to the excess voltage in the battery? Is this where the "float" you mention also comes into play?

I'm going to double check the voltages, while I trace that ground wire. I compared what I found to the schematic and it turns out that the junction block indicated behind the headlight is actually a 4 way bullet connector under the slam panel. It has 3 wires coming out of it, 2 that go to the lights and one being a heavier gauge black wire. This is the wire that must come from the regulator, but the wire at the regulator is a smaller gauge. Now the schematic indicates a joint right before the bullet connectors where it splits off to ground, so this must be where they change the gauge of the wire, and I have no idea why they did this unless the distance to the joint is longer than to the regulator.
Boris

I just rechecked the output and the cutout was wacky again. It was not dropping out when it was supposed to, if at all, so I turned the cam just enough to get the cutout at 13.3 volts and at this setting the dropout activates at about 12 volts.
I think that relay is damaged so I went ahead and ordered a new one. I could probably drive it since I don't see how this could damage the battery at all. If anything it would be safer I would think.

By the way I was idling at 10.5 volts with the lights on and about 11 volts without. The ignition light does not glow when the relay has dropped out, what's the deal? I thought that the light should glow once dropped out.
I'm looking forward to that new regulator.
Boris

Boris,
Just a comment that most consumer voltage meters or multimeters we have available to us (particularly analog units) have a certain % of error in their readings. It won't be much 1-2% usually, but if that fits the variances you see, it may mean that your voltages are "nominally" OK.
Bob Muenchausen

I found where the ground is for the regulator (and lights). There are 2 eyelet connectors with 2 black wires going to each one.
As I mentioned before, one of them has the heavier gauge black wire which is the one I was after. I double checked with a continuity test (I use a miniature digital multimeter).
Both eyelets are bolted under the flasher unit inside the car on the bulkhead.

Still waiting on that regulator.
Boris

Goes to show that schematics are misleading in some cases for illustrative purposes.
Boris

Good post there Paul but it reinforces my question as to why the ignition light does not come on when the cut out relay drops out.
I should receive that regulator today.
Boris

Couple of things. Fist, I realized that I didn't have my WL wire hooked up in order to see the ignition light the other day because my multimeter was attached to it. It does glow now.
Second, I received the voltage regulator today and installed it but the darn thing does not work at all! My multimeter showed .5 to .9 volts and around 1 volt revved up. Now I knew that the volt relay would not cause it but I went ahead and turned the cams and of course it made no difference at all. I even pushed the contacts, still nothing.
But when I went to turn the volt relay cam, my pliers accidentally touched the current relay cam (ground?)and the volts went up to where it should have been!
Tomorrow I am going to test the ground E terminal because it could be that the terminal is not grounded to the base of the regulator correctly.

You know your crazy when you actually find yourself enjoying this.
Boris

I just realized that the current relay is attached to the same base as the volt relay. So what the heck is going on with this thing if by touching the volt relay cam to the current relay cam my voltage is established?

Boris

Unless the volt relay is not properly attached or grounded to the base plate.
Boris

It probably just started to work when you bumped it. That's the first thing you do if the ignition light stays on (whack the unit a little). Did you clean the points? The new ones all have a sticker reminding you to do this, don't they?
Tom

0.5 to 1v dynamo output indicates a faulty dynamo field winding. However if all you have done is changed the control box then either you have got the connections wrong or the 'new' control box is faulty. Clean the current and voltage regulator contacts (normally closed, they are in series and when either is open introduce the current limiting resistor into the field circuit) with a bit of fine wet and dry. Don't wedge anything in them that is thicker than the gap when you operate the relay armature.
Paul Hunt 2

Tom, it is only temporary as long as I touch the volt relay to the current relay. I think the volt relay is not grounded correctly, and this is the new unit.

Paul, the original box is ok, but for the heck of it I did check the output with the field and D terminal connected. The Dynamo is putting out.

I really liked this new unit because the contacts line up perfectly, so I'm going to see if I can fix the ground problem at the volt relay.
Boris

Well I gave up on the new regulator. It definitely is not a ground problem. It must be shorted internally.

Moss Alert, apparently Moss has a return policy that will not reimburse you for shipping, so that's $20 I will never see again.
If you are considering purchasing the type of parts that could be mechanically defective, I would refer you to Victoria British. VB will pay for shipping if the part is at fault.
If you are reading this Moss, a guaranteed way (cough) to lose your customers is to screw them.
Boris

Hi Boris, we were away over the holiday and I just read this thread. You do not seem far away with the old regulator. A floated battery is one which is fully charged and has a voltage applied to it exactly equal to it's fully charged voltage so it takes no current but will always stay fully charged. You need to think of the battery as a chemical energy store to get your head round this. When the cut out is in there is is still an impedance between the B and D terminals so they can be at different voltages. This is the heavy current winding on the cut out and the coil of the over current(with earlier 2 coil regulators this latter is not there of course, this doesn't apply to the MGB which alaways had the more modern 3 coil). With the cut out in but the dynamo volts lower than the battery the current and voltage coils on the cut out are in opposition and will balance out the discharge. When the dynamo comes up to and above battery volts then the current direction reverses in the current winding and the cut out is put firmly on. As dynamo volts drop this will then go back again to opposing eventaully fully open shown by a bright IGN light as the engine revs drop to 0. I drew this out once and would be happy to scan and post it if someone wants to host it.
Stan Best

"A floated battery is one which is fully charged and has a voltage applied to it exactly equal to it's fully charged voltage so it takes no current but will always stay fully charged"

In practical terms this is not true. When under charge in a running vehicle the voltage applied to the battery terminals is typically 14.5v, which drives a constant current through it. This current is controlled by the voltage and current regulator relays to a) prevent overcharging the battery and b) prevent overloading the dynamo respectively . When the engine is switched off the battery voltage will quite quickly drop back to about 12.8v, which *is* its natural fully charged voltage.

I also think you have some of your cut out in's and out's reversed but don't wish to add to the confusion. Suffice to say that when the dynamo voltage drops a certain amount below battery voltage the cut-out relay disconnects the dynamo to prevent it discharging the battery, and when the dynamo volts rises a certain amount above the battery voltage the cut-out relay conncts the dynamo to the battery to charge it again.
Paul Hunt 2

Paul, I was refering to a floated battery "per se" not in a vehicle application.
During charge the acid will be highly concentrated around the pores in the plates, where it is in fact being regenerated, and a voltage in excess of 2.25 per cell can be seen. To float a bettery you would actually keep to this voltage at a current that just creats this concentration gradient. Once all the Lead sulphate is turned back into sulphuric acid you will get gassing of course, at this point you only need to balance leakage and internal discharge. This is what the modern intellgent trickle chargers do.
I have re-read my post and it says exactly what I wanted to about the cut out. The series "current" winding either pulls in or out depending on which way the current is flowing. and this depends on which of the battery or the dynamo is at a higher voltage.
As you say there is no need to understand all this to set up the regulator.
I did mean to post again re an earlier comment from someone else about variable readings.I would like to point out that because a meter is say 2% accurate I would not expect it to give answers varying by that amount every time I measured the same voltage. Repeatabilty is something else and wil be quoted , usually more that an order of magnitude better than claimed absolute accuracy. If going out on site I would not take a sub-standard but rather check a lab meter against one and take that with a graph, relying on repeatabilty.
Stan Best

thanks guys, I am one to push my envelope and for me, electronics can be that. Im going to be ordering another regulator from VB, but for now im working on my other classic.
Boris

This thread was discussed between 22/12/2005 and 04/01/2006

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